1) What is difference
between JDK,JRE and JVM?
JVM
JVM is an acronym for Java
Virtual Machine, it is an abstract machine which provides the runtime
environment in which java bytecode can be executed. It is a specification.
JVMs are available for many
hardware and software platforms (so JVM is platform dependent).
JRE
JRE stands for Java Runtime
Environment. It is the implementation of JVM.
JDK
JDK is an acronym for Java
Development Kit. It physically exists. It contains JRE + development tools.
2) How many types of
memory areas are allocated by JVM?
Many types:
- Class(Method) Area
- Heap
- Stack
- Program Counter Register
- Native Method Stack
3) What is JIT
compiler?
Just-In-Time(JIT)
compiler:It is used to improve the performance. JIT compiles parts of the
byte code that have similar functionality at the same time, and hence reduces
the amount of time needed for compilation.Here the term “compiler” refers to a
translator from the instruction set of a Java virtual machine (JVM) to the
instruction set of a specific CPU.
4) What is platform?
A platform is basically the
hardware or software environment in which a program runs. There are two types
of platforms software-based and hardware-based. Java provides software-based
platform.
5) What is the main
difference between Java platform and other platforms?
The Java platform differs
from most other platforms in the sense that it's a software-based platform that
runs on top of other hardware-based platforms.It has two components:
- Runtime Environment
- API(Application Programming
Interface)
6) What gives Java its
'write once and run anywhere' nature?
The bytecode. Java is
compiled to be a byte code which is the intermediate language between source code
and machine code. This byte code is not platform specific and hence can be fed
to any platform.
7) What is
classloader?
The classloader is a
subsystem of JVM that is used to load classes and interfaces.There are many
types of classloaders e.g. Bootstrap classloader, Extension classloader, System
classloader, Plugin classloader etc.
8) Is Empty .java file
name a valid source file name?
Yes, save your java file by
.java only, compile it by javac .java and run by java
yourclassname Let's take a simple example:
1.
//save by .java only
2.
class A{
3.
public static void main(String args[]){
4.
System.out.println("Hello java");
5.
}
6.
}
7.
//compile by javac .java
8. //run by java A
compile it by javac
.java
run it by java A
9) Is delete,next,main,exit
or null keyword in java?
No.
10) If I don't provide
any arguments on the command line, then the String array of Main method will be
empty or null?
It is empty. But not null.
11) What if I write
static public void instead of public static void?
Program compiles and runs
properly.
12) What is the
default value of the local variables?
The local variables are not
initialized to any default value, neither primitives nor object references.
Core Java - OOPs
Concepts: Initial OOPs Interview Questions
There
is given more than 50 OOPs (Object-Oriented Programming and System) interview
questions. But they have been categorized in many sections such as constructor
interview questions, static interview questions, Inheritance Interview questions,
Abstraction interview question, Polymorphism interview questions etc. for
better understanding.
13)
What is difference between object oriented programming language and object
based programming language?
Object
based programming languages follow all the features of OOPs except Inheritance.
Examples of object based programming languages are JavaScript, VBScript etc.
14)
What will be the initial value of an object reference which is defined as an
instance variable?
The
object references are all initialized to null in Java.
Core Java - OOPs
Concepts: Constructor Interview Questions
15)
What is constructor?
- Constructor
is just like a method that is used to initialize the state of an object.
It is invoked at the time of object creation.
16)
What is the purpose of default constructor?
- The
default constructor provides the default values to the objects. The java
compiler creates a default constructor only if there is no constructor in
the class.more details...
17)
Does constructor return any value?
Ans:yes,
that is current instance (You cannot use return type yet it returns a value).more
details...
18)Is
constructor inherited?
No,
constructor is not inherited.
19)
Can you make a constructor final?
No,
constructor can't be final.
Core Java - OOPs
Concepts: static keyword Interview Questions
20)
What is static variable?
- static
variable is used to refer the common property of all objects (that is not
unique for each object) e.g. company name of employees,college name of
students etc.
- static
variable gets memory only once in class area at the time of class loading.
21)
What is static method?
- A static
method belongs to the class rather than object of a class.
- A static
method can be invoked without the need for creating an instance of a
class.
- static
method can access static data member and can change the value of it.
22)
Why main method is static?
because
object is not required to call static method if It were non-static method,jvm
creats object first then call main() method that will lead to the problem of
extra memory allocation.more details...
23)
What is static block?
- Is used to
initialize the static data member.
- It is
excuted before main method at the time of classloading.
24)
Can we execute a program without main() method?
Ans)
Yes, one of the way is static block.more details...
25)
What if the static modifier is removed from the signature of the main method?
Program
compiles. But at runtime throws an error "NoSuchMethodError".
26)
What is difference between static (class) method and instance method?
|
static or class method
|
instance method
|
|
1)A
method i.e. declared as static is known as static method.
|
A
method i.e. not declared as static is known as instance method.
|
|
2)Object
is not required to call static method.
|
Object
is required to call instance methods.
|
|
3)Non-static
(instance) members cannot be accessed in static context (static method,
static block and static nested class) directly.
|
static
and non-static variables both can be accessed in instance methods.
|
|
4)For
example: public static int cube(int n){ return n*n*n;}
|
For
example: public void msg(){...}.
|
Core Java - OOPs
Concepts: Inheritance Interview Questions
27)
What is this in java?
It
is a keyword that that refers to the current object.more
details...
28)What
is Inheritance?
Inheritance
is a mechanism in which one object acquires all the properties and behaviour of
another object of another class. It represents IS-A relationship. It is used
for Code Resusability and Method Overriding.
29)
Which class is the superclass for every class.
Object
class.
30)
Why multiple inheritance is not supported in java?
- To reduce
the complexity and simplify the language, multiple inheritance is not
supported in java in case of class.more details...
31)
What is composition?
Holding
the reference of the other class within some other class is known as
composition.
32)
What is difference between aggregation and composition?
Aggregation
represents weak relationship whereas composition represents strong
relationship. For example: bike has an indicator (aggregation) but bike has an
engine (compostion).
33)
Why Java does not support pointers?
Pointer
is a variable that refers to the memory address. They are not used in java
because they are unsafe(unsecured) and complex to understand.
34)
What is super in java?
It
is a keyword that refers to the immediate parent class object.more
details...
35)
Can you use this() and super() both in a constructor?
No.
Because super() or this() must be the first statement.
36)What
is object cloning?
The
object cloning is used to create the exact copy of an object. more
details...
Core Java - OOPs
Concepts: Method Overloading Interview Questions
37)
What is method overloading?
If
a class have multiple methods by same name but different parameters, it is
known as Method Overloading. It increases the readability of the program.more details...
38)
Why method overloading is not possible by changing the return type in java?
Becauseof
ambiguity.more details...
39)
Can we overload main() method?
Yes,
You can have many main() methods in a class by overloading the main method.
Core Java - OOPs
Concepts: Method Overriding Interview Questions
40)
What is method overriding:
If
a subclass provides a specific implementation of a method that is already
provided by its parent class, it is known as Method Overriding. It is used for
runtime polymorphism and to provide the specific implementation of the method.more details...
41)
Can we override static method?
No,
you can't override the static method because they are the part of class not
object.
42)
Why we cannot override static method?
It
is because the static method is the part of class and it is bound with class
whereas instance method is bound with object and static gets memory in class
area and instance gets memory in heap.
43)
Can we override the overloaded method?
Yes.
44)
Difference between method Overloading and Overriding.
|
Method Overloading
|
Method Overriding
|
|
1)
Method overloading increases the readability of the program.
|
Method
overriding provides the specific implementation of the method that is already
provided by its super class.
|
|
2)
method overlaoding is occurs within the class.
|
Method
overriding occurs in two classes that have IS-A relationship.
|
|
3) In
this case, parameter must be different.
|
In this
case, parameter must be same.
|
45)
Can you have virtual functions in Java?
Yes,
all functions in Java are virtual by default.
46)
What is covariant return type?
Now,
since java5, it is possible to override any method by changing the return type
if the return type of the subclass overriding method is subclass type. It is
known as covariant return type. more
details...
Core Java - OOPs
Concepts: final keyword Interview Questions
47)
What is final variable?
If
you make any variable as final, you cannot change the value of final
variable(It will be constant).more details...
48)
What is final method?
Final
methods can't be overriden.more details...
49)
What is final class?
Final
class can't be inherited. more details...
50)
What is blank final variable?
A
final variable, not initalized at the time of declaration, is known as blank
final variable.more details...
51)
Can we intialize blank final variable?
Yes,
only in constructor if it is non-static. If it is static blank final variable,
it can be initialized only in the static block.more
details...
52)
Can you declare the main method as final?
Yes,
such as, public static final void main(String[] args){}.
53) What is Runtime Polymorphism?
Runtime polymorphism or dynamic
method dispatch is a process in which a call to an overridden method is
resolved at runtime rather than at compile-time.
In this process, an overridden
method is called through the reference variable of a super class. The
determination of the method to be called is based on the object being referred
to by the reference variable.
54) Can you achieve Runtime Polymorphism by data members?
No.
55) What is the difference between static binding and
dynamic binding?
In case of static binding type
of object is determined at compile time whereas in dynamic binding type of
object is determined at runtime.
Core Java - OOPs Concepts : Abstraction Interview Questions
56) What is abstraction?
Abstraction
is a process of hiding the implementation details and showing only
functionality to the user.
Abstraction
lets you focus on what the object does instead of how it does it.
57) What is the difference between
abstraction and encapsulation?
Abstraction
hides the implementation details whereas encapsulation wraps code and data into
a single unit.
58) What is abstract class?
A class
that is declared as abstract is known as abstract class. It needs to be
extended and its method implemented. It cannot be instantiated.
59) Can there be any abstract
method without abstract class?
No, if
there is any abstract method in a class, that class must be abstract.
60) Can you use abstract and final
both with a method?
No,
because abstract method needs to be overridden whereas you can't override final
method.
61) Is it possible to instantiate
the abstract class?
No,
abstract class can never be instantiated.
62) What is interface?
Interface
is a blueprint of a class that have static constants and abstract methods.It
can be used to achieve fully abstraction and multiple inheritance.
63) Can you declare an interface
method static?
No,
because methods of an interface is abstract by default, and static and abstract
keywords can't be used together.
64) Can an Interface be final?
No,
because its implementation is provided by another class.
65) What is marker interface?
An
interface that have no data member and method is known as a marker
interface.For example Serializable, Cloneable etc.
66) What is difference between
abstract class and interface?
|
Abstract class
|
Interface
|
|
1)An abstract class can have method body (non-abstract methods).
|
Interface have only abstract methods.
|
|
2)An abstract class can have instance variables.
|
An interface cannot have instance variables.
|
|
3)An abstract class can have constructor.
|
Interface cannot have constructor.
|
|
4)An abstract class can have static methods.
|
Interface cannot have static methods.
|
|
5)You can extends one abstract class.
|
You can implement multiple interfaces.
|
67) Can we define private and
protected modifiers for variables in interfaces?
No,
they are implicitly public.
68) When can an object reference be
cast to an interface reference?
An
object reference can be cast to an interface reference when the object
implements the referenced interface.
Core Java - OOPs Concepts : Package
Interview Questions
69) What is package?
A
package is a group of similar type of classes interfaces and sub-packages. It
provides access protection and removes naming collision.
70) Do I need to import java.lang
package any time? Why ?
No. It
is by default loaded internally by the JVM.
71) Can I import same package/class
twice? Will the JVM load the package twice at runtime?
One can
import the same package or same class multiple times. Neither compiler nor JVM
complains about it.But the JVM will internally load the class only once no
matter how many times you import the same class.
72) What is static import ?
By
static import, we can access the static members of a class directly, there is
no to qualify it with the class name.
73) What is Exception
Handling?
Exception Handling is a
mechanism to handle runtime errors.It is mainly used to handle checked
exceptions.
74) What is difference
between Checked Exception and Unchecked Exception?
1)Checked Exception
The classes that extend
Throwable class except RuntimeException and Error are known as checked
exceptions e.g.IOException,SQLException etc. Checked exceptions are checked at
compile-time.
2)Unchecked Exception
The classes that extend
RuntimeException are known as unchecked exceptions e.g. ArithmeticException,NullPointerException
etc. Unchecked exceptions are not checked at compile-time.
75) What is the base
class for Error and Exception?
Throwable.
76) Is it necessary
that each try block must be followed by a catch block?
It is not necessary that
each try block must be followed by a catch block. It should be followed by
either a catch block OR a finally block. And whatever exceptions are likely to
be thrown should be declared in the throws clause of the method.
77) What is finally
block?
- finally block is a block that is
always executed.more
details...
78) Can finally block
be used without catch?
- Yes, by try block. finally must be
followed by either try or catch.more
details...
79) Is there any case
when finally will not be executed?
finally block will not be
executed if program exits(either by calling System.exit() or by causing a fatal
error that causes the process to abort).more
details...
80) What is difference
between throw and throws?
|
throw keyword
|
throws keyword
|
|
1)throw
is used to explicitly throw an exception.
|
throws
is used to declare an exception.
|
|
2)checked
exceptions can not be propagated with throw only.
|
checked
exception can be propagated with throws.
|
|
3)throw
is followed by an instance.
|
throws
is followed by class.
|
|
4)throw
is used within the method.
|
throws
is used with the method signature.
|
|
5)You
cannot throw multiple exception
|
You can
declare multiple exception e.g. public void method()throws
IOException,SQLException.
|
81) Can an exception
be rethrown?
Yes.
82) Can subclass
overriding method declare an exception if parent class method doesn't throw an
exception ?
Yes but only unchecked
exception not checked.
83) What is exception
propagation ?
Forwarding the exception
object to the invoking method is known as exception propagation.
There
is given a list of string handling interview questions with short and pointed
answers. If you know any string handling interview question, kindly post it in
the comment section.
84)
What is the meaning of immutable in terms of String?
The
simple meaning of immutable is unmodifiable or unchangeable. Once string object
has been created, its value can't be changed.
85)
Why string objects are immutable in java?
Because
java uses the concept of string literal. Suppose there are 5 reference
variables,all referes to one object "sachin".If one reference
variable changes the value of the object, it will be affected to all the
reference variables. That is why string objects are immutable in java.
86)
How many ways we can create the string object?
There
are two ways to create the string object, by string literal and by new keyword.
87)
How many objects will be created in the following code?
1.
String s1="Welcome";
2.
String s2="Welcome";
3. String s3="Welcome";
Only
one object.
88)
Why java uses the concept of string literal?
To
make Java more memory efficient (because no new objects are created if it
exists already in string constant pool).
89)How
many objects will be created in the following code?
1. String s = new String("Welcome");
Two
objects, one in string constant pool and other in non-pool(heap).
90)
What is the basic difference between string and stringbuffer object?
String
is an immutable object. StringBuffer is a mutable object.
91)
What is the difference between StringBuffer and StringBuilder ?
StringBuffer
is synchronized whereas StringBuilder is not synchronized.
92)
How can we create immutable class in java ?
We
can create immutable class as the String class by defining final class and
93)
What is the purpose of toString() method in java ?
The
toString() method returns the string representation of any object. If you print
any object, java compiler internally invokes the toString() method on the
object. So overriding the toString() method, returns the desired output, it can
be the state of an object etc. depends on your implementation.
Core Java : Nested
classes and Interfaces Interview Questions
94)What
is nested class?
A
class which is declared inside another class is known as nested class. There
are 4 types of nested class member inner class, local inner class, annonymous
inner class and static nested class.
95)
Is there any difference between nested classes and inner classes?
Yes,
inner classes are non-static nested classes i.e. inner classes are the part of
nested classes.
96)
Can we access the non-final local variable, inside the local inner class?
No,
local variable must be constant if you want to access it in local inner class.
97)
What is nested interface ?
Any
interface i.e. declared inside the interface or class, is known as nested
interface. It is static by default.
98)
Can a class have an interface?
Yes,
it is known as nested interface.
99)
Can an Interface have a class?
Yes,
they are static implicitely.
117) What is Garbage
Collection?
Garbage collection is a
process of reclaiming the runtime unused objects.It is performed for memory
management.
118) What is gc()?
gc() is a daemon
thread.gc() method is defined in System class that is used to send request to
JVM to perform garbage collection.
119) What is the
purpose of finalize() method?
finalize() method is
invoked just before the object is garbage collected.It is used to perform
cleanup processing.
120) Can an
unrefrenced objects be refrenced again?
Yes.
121)What kind of
thread is the Garbage collector thread?
Daemon thread.
122)What is difference
between final, finally and finalize?
|
final: final
is a keyword, final can be variable, method or class.You, can't change the
value of final variable, can't override final method, can't inherit final
class.
|
|
finally: finally
block is used in exception handling. finally block is always executed.
|
|
finalize():finalize()
method is used in garbage collection.finalize() method is invoked just before
the object is garbage collected.The finalize() method can be used to perform
any cleanup processing.
|
123)What is the
purpose of the Runtime class?
The purpose of the Runtime
class is to provide access to the Java runtime system.
124)How will you
invoke any external process in Java?
By
Runtime.getRuntime().exec(?) method.
I/O Interview Questions
125)What
is the difference between the Reader/Writer class hierarchy and the
InputStream/OutputStream class hierarchy?
The
Reader/Writer class hierarchy is character-oriented, and the
InputStream/OutputStream class hierarchy is byte-oriented.
126)What
an I/O filter?
An
I/O filter is an object that reads from one stream and writes to another,
usually altering the data in some way as it is passed from one stream to
another.
Serialization Interview
Questions
127)
What is serialization?
Serialization
is a process of writing the state of an object into a byte stream.It is mainly
used to travel object's state on the network.
128)
What is Deserialization?
Deserialization
is the process of reconstructing the object from the serialized state.It is the
reverse operation of serialization.
129)
What is transient keyword?
If
you define any data member as transient,it will not be serialized.more
details...
130)What
is Externalizable?
Externalizable
interface is used to write the state of an object into a byte stream in
compressed format.It is not a marker interface.
131)What
is the difference between Serializalble and Externalizable interface?
Serializable
is a marker interface but Externalizable is not a marker interface.When you use
Serializable interface, your class is serialized automatically by default. But
you can override writeObject() and readObject() two methods to control more
complex object serailization process. When you use Externalizable interface,
you have a complete control over your class's serialization process.
Networking Interview
Questions
132)How
do I convert a numeric IP address like 192.18.97.39 into a hostname like
java.sun.com?
By
InetAddress.getByName("192.18.97.39").getHostName() where
192.18.97.39 is the IP address.
Reflection Interview
Questions
133)
What is reflection?
Reflection
is the process of examining or modifying the runtime behaviour of a class at
runtime.It is used in:
- IDE
(Integreted Development Environment) e.g. Eclipse, MyEclipse, NetBeans.
- Debugger
- Test Tools
etc.
134)
Can you access the private method from outside the class?
Yes,
by changing the runtime behaviour of a class if the class is not secured.
148)What are wrapper classes?
Wrapper classes are classes
that allow primitive types to be accessed as objects.
149)What is a native method?
A native method is a method
that is implemented in a language other than Java.
150)What is the purpose of the System class?
The purpose of the System class
is to provide access to system resources.
151)What comes to mind when someone mentions a shallow copy
in Java?
Object cloning.
152)What is singleton class?
Singleton class means that any
given time only one instance of the class is present, in one JVM.
AWT and SWING Interview Questions
153)Which containers use a border
layout as their default layout?
The Window,
Frame and Dialog classes use a border layout as their default layout.
154)Which containers use a
FlowLayout as their default layout?
The
Panel and Applet classes use the FlowLayout as their default layout.
155)What are peerless components?
The
peerless components are called light weight components.
156)is the difference between a
Scrollbar and a ScrollPane?
A
Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A
ScrollPane handles its own events and performs its own scrolling.
157)What is a lightweight
component?
Lightweight
components are the one which doesn?t go with the native call to obtain the
graphical units. They share their parent component graphical units to render
them. For example, Swing components.
158)What is a heavyweight
component?
For
every paint call, there will be a native call to get the graphical units.For
Example, AWT.
159)What is an applet?
An
applet is a small java program that runs inside the browser and generates
dynamic contents.
160)Can you write a Java class that
could be used both as an applet as well as an application?
Yes.
Add a main() method to the applet.
Internationalization Interview
Questions
161)What is Locale?
A
Locale object represents a specific geographical, political, or cultural region.
162)How will you load a specific
locale?
By
ResourceBundle.getBundle(?) method.
Java Bean Interview Questions
163)What is a JavaBean?
are
reusable software components written in the Java programming language, designed
to be manipulated visually by a software development environment, like JBuilder
or VisualAge for Java.
RMI Interview Questions
164)Can RMI and Corba based
applications interact?
Yes
they can. RMI is available with IIOP as the transport protocol instead of JRMP.
1) What is
multithreading?
Multithreading is a process
of executing multiple threads simultaneously. Its main advantage is:
- Threads share the same address
space.
- Thread is lightweight.
- Cost of communication between
process is low.
2) What is thread?
A thread is a lightweight
subprocess.It is a separate path of execution.It is called separate path of
execution because each thread runs in a separate stack frame.
3)What is the
difference between preemptive scheduling and time slicing?
Under preemptive
scheduling, the highest priority task executes until it enters the waiting or
dead states or a higher priority task comes into existence. Under time slicing,
a task executes for a predefined slice of time and then reenters the pool of
ready tasks. The scheduler then determines which task should execute next,
based on priority and other factors.
4) What does join()
method?
The join() method waits for
a thread to die. In other words, it causes the currently running threads to
stop executing until the thread it joins with completes its task.
5) What is difference
between wait() and sleep() method?
|
wait()
|
sleep()
|
|
1) The
wait() method is defined in Object class.
|
The
sleep() method is defined in Thread class.
|
|
2)
wait() method releases the lock.
|
The
sleep() method doesn't releases the lock.
|
6)
Is it possible to start a thread twice?
No,
there is no possibility to start a thread twice. If we does, it throws an
exception.
7)
Can we call the run() method instead of start()?
yes,
but it will not work as a thread rather it will work as a normal object so
there will not be context-switching between the threads.
8)
What about the daemon threads?
The
daemon threads are basically the low priority threads that provides the
background support to the user threads. It provides services to the user
threads.
9)Can
we make the user thread as daemon thread if thread is started?
No,
if you do so, it will throw IllegalThreadStateException
10)What
is shutdown hook?
The
shutdown hook is basically a thread i.e. invoked implicitely before JVM shuts
down. So we can use it perform clean up resource.
11)When
should we interrupt a thread?
We
should interrupt a thread if we want to break out the sleep or wait state of a
thread.
12)
What is synchronization?
Synchronization
is the capabilility of control the access of multiple threads to any shared
resource.It is used:
- To prevent
thread interference.
- To prevent
consistency problem.
13)
What is the purpose of Synchronized block?
- Synchronized
block is used to lock an object for any shared resource.
- Scope of synchronized
block is smaller than the method.
14)Can
Java object be locked down for exclusive use by a given thread?
Yes.
You can lock an object by putting it in a "synchronized" block. The
locked object is inaccessible to any thread other than the one that explicitly
claimed it.
15)
What is static synchronization?
If
you make any static method as synchronized, the lock will be on the class not
on object. more details...
16)What
is the difference between notify() and notifyAll()?
The
notify() is used to unblock one waiting thread whereas notifyAll() method is
used to unblock all the threads in waiting state.
17)What
is deadlock?
Deadlock
is a situation when two threads are waiting on each other to release a
resource. Each thread waiting for a resource which is held by the other waiting
thread.
20 Java Collections Interview Questions
In java, collection interview
questions are mostly asked by the interviewers. Here is the list of mostly
asked collections interview questions with answers.
1) What is the difference between ArrayList and Vector?
|
No.
|
ArrayList
|
Vector
|
|
1)
|
ArrayList is not synchronized.
|
Vector is synchronized.
|
|
2)
|
ArrayList is not a legacy class.
|
Vector is a legacy class.
|
|
3)
|
ArrayList increases its size by 50% of the array size.
|
Vector increases its size by doubling the array size.
|
2) What is the difference between ArrayList and LinkedList?
|
No.
|
ArrayList
|
LinkedList
|
|
1)
|
ArrayList uses a dynamic array.
|
LinkedList uses doubly linked list.
|
|
2)
|
ArrayList is not efficient for manipulation because a lot of
shifting is required.
|
LinkedList is efficient for manipulation.
|
|
3)
|
ArrayList is better to store and fetch data.
|
LinkedList is better to manipulate data.
|
3) What is the difference between Iterator and
ListIterator?
Iterator traverses the elements
in forward direction only whereas ListIterator traverses the elements in
forward and backward direction.
|
No.
|
Iterator
|
ListIterator
|
|
1)
|
Iterator traverses the elements in forward direction only.
|
ListIterator traverses the elements in backward and forward
directions both.
|
|
2)
|
Iterator can be used in List, Set and Queue.
|
ListIterator can be used in List only.
|
4) What is the difference between Iterator and Enumeration?
|
No.
|
Iterator
|
Enumeration
|
|
1)
|
Iterator can traverse legacy and non-legacy elements.
|
Enumeration can traverse only legacy elements.
|
|
2)
|
Iterator is fail-fast.
|
Enumeration is not fail-fast.
|
|
3)
|
Iterator is slower than Enumeration.
|
Enumeration is faster than Iterator.
|
5) What is the difference between List and Set?
List can contain duplicate
elements whereas Set contains only unique elements.
6) What is the difference between
HashSet and TreeSet?
HashSet
maintains no order whereas TreeSet maintains ascending order.
7) What is the difference between
Set and Map?
Set
contains values only whereas Map contains key and values both.
8) What is the difference between
HashSet and HashMap?
HashSet
contains only values whereas HashMap contains entry(key,value). HashSet can be
iterated but HashMap need to convert into Set to be iterated.
9) What is the difference between HashMap
and TreeMap?
HashMap
maintains no order but TreeMap maintains ascending order.
10) What is the difference between
HashMap and Hashtable?
|
No.
|
HashMap
|
Hashtable
|
|
1)
|
HashMap is not synchronized.
|
Hashtable is synchronized.
|
|
2)
|
HashMap can contain one null key and multiple null values.
|
Hashtable cannot contain any null key or null value.
|
11) What is the difference between
Collection and Collections?
Collection
is an interface whereas Collections is a class. Collection interface provides
normal functionality of data structure to List, Set and Queue. But, Collections
class is to sort and synchronize collection elements.
12) What is the difference between
Comparable and Comparator?
|
No.
|
Comparable
|
Comparator
|
|
1)
|
Comparable provides only one sort of sequence.
|
Comparator provides multiple sort of sequences.
|
|
2)
|
It provides one method named compareTo().
|
It provides one method named compare().
|
|
3)
|
It is found in java.lang package.
|
it is found in java.util package.
|
|
4)
|
If we implement Comparable interface, actual class is modified.
|
Actual class is not modified.
|
13) What is the advantage of
Properties file?
If you
change the value in properties file, you don't need to recompile the java
class. So, it makes the application easy to manage.
14) What does the hashCode()
method?
The
hashCode() method returns a hash code value (an integer number).
The
hashCode() method returns the same integer number, if two keys (by calling
equals() method) are same.
But, it
is possible that two hash code numbers can have different or same keys.
15) Why we override equals()
method?
The
equals method is used to check whether two objects are same or not. It needs to
be overridden if we want to check the objects based on property.
For
example, Employee is a class that has 3 data members: id, name and salary. But,
we want to check the equality of employee object on the basis of salary. Then,
we need to override the equals() method.
16) How to synchronize List, Set
and Map elements?
Yes,
Collections class provides methods to make List, Set or Map elements as
synchronized:
|
public static List synchronizedList(List l){}
|
|
public static Set synchronizedSet(Set s){}
|
|
public static SortedSet synchronizedSortedSet(SortedSet s){}
|
|
public static Map synchronizedMap(Map m){}
|
|
public static SortedMap synchronizedSortedMap(SortedMap m){}
|
17) What is the advantage of
generic collection?
If we
use generic class, we don't need typecasting. It is typesafe and checked at
compile time.
18) What is hash-collision in
Hashtable and how it is handled in Java?
Two
different keys with the same hash value is known as hash-collision. Two
different entries will be kept in a single hash bucket to avoid the collision.
19) What is the Dictionary class?
The
Dictionary class provides the capability to store key-value pairs.
20) What is the default size of
load factor in hashing based collection?
The
default size of load factor is 0.75.
The default capacity is computed as initial capacity * load factor. For
example, 16 * 0.75 = 12. So, 12 is the default capacity of Map.
20 Java Collections Interview Questions
In java, collection interview
questions are mostly asked by the interviewers. Here is the list of mostly
asked collections interview questions with answers.
1) What is the difference between ArrayList and Vector?
|
No.
|
ArrayList
|
Vector
|
|
1)
|
ArrayList is not synchronized.
|
Vector is synchronized.
|
|
2)
|
ArrayList is not a legacy class.
|
Vector is a legacy class.
|
|
3)
|
ArrayList increases its size by 50% of the array size.
|
Vector increases its size by doubling the array size.
|
2) What is the difference between ArrayList and LinkedList?
|
No.
|
ArrayList
|
LinkedList
|
|
1)
|
ArrayList uses a dynamic array.
|
LinkedList uses doubly linked list.
|
|
2)
|
ArrayList is not efficient for manipulation because a lot of
shifting is required.
|
LinkedList is efficient for manipulation.
|
|
3)
|
ArrayList is better to store and fetch data.
|
LinkedList is better to manipulate data.
|
3) What is the difference between Iterator and
ListIterator?
Iterator traverses the elements
in forward direction only whereas ListIterator traverses the elements in
forward and backward direction.
|
No.
|
Iterator
|
ListIterator
|
|
1)
|
Iterator traverses the elements in forward direction only.
|
ListIterator traverses the elements in backward and forward
directions both.
|
|
2)
|
Iterator can be used in List, Set and Queue.
|
ListIterator can be used in List only.
|
4) What is the difference between Iterator and Enumeration?
|
No.
|
Iterator
|
Enumeration
|
|
1)
|
Iterator can traverse legacy and non-legacy elements.
|
Enumeration can traverse only legacy elements.
|
|
2)
|
Iterator is fail-fast.
|
Enumeration is not fail-fast.
|
|
3)
|
Iterator is slower than Enumeration.
|
Enumeration is faster than Iterator.
|
5) What is the difference between List and Set?
List can contain duplicate
elements whereas Set contains only unique elements.
6) What is the difference between
HashSet and TreeSet?
HashSet
maintains no order whereas TreeSet maintains ascending order.
7) What is the difference between
Set and Map?
Set
contains values only whereas Map contains key and values both.
8) What is the difference between
HashSet and HashMap?
HashSet
contains only values whereas HashMap contains entry(key,value). HashSet can be
iterated but HashMap need to convert into Set to be iterated.
9) What is the difference between
HashMap and TreeMap?
HashMap
maintains no order but TreeMap maintains ascending order.
10) What is the difference between
HashMap and Hashtable?
|
No.
|
HashMap
|
Hashtable
|
|
1)
|
HashMap is not synchronized.
|
Hashtable is synchronized.
|
|
2)
|
HashMap can contain one null key and multiple null values.
|
Hashtable cannot contain any null key or null value.
|
11) What is the difference between
Collection and Collections?
Collection
is an interface whereas Collections is a class. Collection interface provides
normal functionality of data structure to List, Set and Queue. But, Collections
class is to sort and synchronize collection elements.
12) What is the difference between
Comparable and Comparator?
|
No.
|
Comparable
|
Comparator
|
|
1)
|
Comparable provides only one sort of sequence.
|
Comparator provides multiple sort of sequences.
|
|
2)
|
It provides one method named compareTo().
|
It provides one method named compare().
|
|
3)
|
It is found in java.lang package.
|
it is found in java.util package.
|
|
4)
|
If we implement Comparable interface, actual class is modified.
|
Actual class is not modified.
|
13) What is the advantage of
Properties file?
If you
change the value in properties file, you don't need to recompile the java
class. So, it makes the application easy to manage.
14) What does the hashCode()
method?
The
hashCode() method returns a hash code value (an integer number).
The
hashCode() method returns the same integer number, if two keys (by calling
equals() method) are same.
But, it
is possible that two hash code numbers can have different or same keys.
15) Why we override equals()
method?
The
equals method is used to check whether two objects are same or not. It needs to
be overridden if we want to check the objects based on property.
For
example, Employee is a class that has 3 data members: id, name and salary. But,
we want to check the equality of employee object on the basis of salary. Then,
we need to override the equals() method.
16) How to synchronize List, Set
and Map elements?
Yes,
Collections class provides methods to make List, Set or Map elements as
synchronized:
|
public static List synchronizedList(List l){}
|
|
public static Set synchronizedSet(Set s){}
|
|
public static SortedSet synchronizedSortedSet(SortedSet s){}
|
|
public static Map synchronizedMap(Map m){}
|
|
public static SortedMap synchronizedSortedMap(SortedMap m){}
|
17) What is the advantage of
generic collection?
If we
use generic class, we don't need typecasting. It is typesafe and checked at
compile time.
18) What is hash-collision in
Hashtable and how it is handled in Java?
Two
different keys with the same hash value is known as hash-collision. Two
different entries will be kept in a single hash bucket to avoid the collision.
19) What is the Dictionary class?
The
Dictionary class provides the capability to store key-value pairs.
20) What is the default size of
load factor in hashing based collection?
The
default size of load factor is 0.75.
The default capacity is computed as initial capacity * load factor. For
example, 16 * 0.75 = 12. So, 12 is the default capacity of Map.
1) How many objects of
a servlet is created?
Only one object at the time
of first request by servlet or web container.
2) What is the
life-cycle of a servlet?
- Servlet is loaded
- servlet is instantiated
- servlet is initialized
- service the request
- servlet is destroyed
3) What are the life-cycle
methods for a servlet?
|
Method
|
Description
|
|
public
void init(ServletConfig config)
|
It is
invoked only once when first request comes for the servlet. It is used to
initialize the servlet.
|
|
public
void service(ServletRequest request,ServletResponse)throws
ServletException,IOException
|
It is
invoked at each request.The service() method is used to service the request.
|
|
public
void destroy()
|
It is
invoked only once when servlet is unloaded.
|
4) Who is responsible
to create the object of servlet?
The web container or
servlet container.
5) When servlet object
is created?
At the time of first
request.
6)
What is difference between Get and Post method?
|
Get
|
Post
|
|
1)
Limited amount of data can be sent because data is sent in header.
|
Large
amount of data can be sent because data is sent in body.
|
|
2) Not
Secured because data is exposed in URL bar.
|
Secured
because data is not exposed in URL bar.
|
|
3) Can
be bookmarked
|
Cannot
be bookmarked
|
|
4)
Idempotent
|
Non-Idempotent
|
|
5) It
is more efficient and used than Post
|
It is
less efficient and used
|
7)
What is difference between PrintWriter and ServletOutputStream?
PrintWriter
is a character-stream class where as ServletOutputStream is a byte-stream
class. The PrintWriter class can be used to write only character-based
information whereas ServletOutputStream class can be used to write primitive
values as well as character-based information.
8)
What is difference between GenericServlet and HttpServlet?
The
GenericServlet is protocol independent whereas HttpServlet is HTTP protocol
specific. HttpServlet provides additional functionalities such as state
management etc.
9)
What is servlet collaboration?
When
one servlet communicates to another servlet, it is known as servlet
collaboration. There are many ways of servlet collaboration:
- RequestDispacher
interface
- sendRedirect()
method etc.
10)
What is the purpose of RequestDispatcher Interface?
The
RequestDispacher interface provides the facility of dispatching the request to
another resource it may be html, servlet or jsp. This interceptor can also be
used to include the content of antoher resource.
11)
Can you call a jsp from the servlet?
Yes,
one of the way is RequestDispatcher interface for example:
1.
RequestDispatcher rd=request.getRequestDispatcher("/login.jsp");
2. rd.forward(request,response);
12)
Difference between forward() method and sendRedirect() method ?
|
forward() method
|
sendRedirect() method
|
|
1)
forward() sends the same request to another resource.
|
1) sendRedirect()
method sends new request always because it uses the URL bar of the browser.
|
|
2)
forward() method works at server side.
|
2)
sendRedirect() method works at client side.
|
|
3)
forward() method works within the server only.
|
3)
sendRedirect() method works within and outside the server.
|
13)
What is difference between ServletConfig and ServletContext?
The
container creates object of ServletConfig for each servlet whereas object of
ServletContext is created for each web application.
14)
What is Session Tracking?
Session simply
means a particular interval of time.
Session
Tracking is a way to maintain state of an user.Http protocol is a stateless
protocol.Each time user requests to the server, server treats the request as
the new request.So we need to maintain the state of an user to recognize to
particular user.
15)
What are Cookies?
A
cookie is a small piece of information that is persisted between the multiple
client requests. A cookie has a name, a single value, and optional attributes
such as a comment, path and domain qualifiers, a maximum age, and a version
number.
16)
What is difference between Cookies and HttpSession?
Cookie
works at client side whereas HttpSession works at server side.
17)
What is filter?
A
filter is an object that is invoked either at the preprocessing or
postprocessing of a request. It is pluggable.
18)
How can we perform any action at the time of deploying the project?
By
the help of ServletContextListener interface.
19)
What is the disadvantage of cookies?
It
will not work if cookie is disabled from the browser.
20)
How can we upload the file to the server using servlet?
One
of the way is by MultipartRequest class provided by third party.
21)
What is load-on-startup in servlet?
The
load-on-startup element of servlet in web.xml is used to load the servlet at
the time of deploying the project or server start. So it saves time for the
response of first request.
22)
What if we pass negative value in load-on-startup?
It
will not affect the container, now servlet will be loaded at first request.
23)
What is war file?
A
war (web archive) file specifies the web elements. A servlet or jsp project can
be converted into a war file. Moving one servlet project from one place to
another will be fast as it is combined into a single file.
24)
How to create war file?
The
war file can be created using jar tool found in jdk/bin directory. If you are
using Eclipse or Netbeans IDE, you can export your project as a war file.
To
create war file from console, you can write following code.
1. jar -cvf abc.war *
Now
all the files of current directory will be converted into abc.war file.
25)
What are the annotations used in Servlet 3?
There
are mainly 3 annotations used for the servlet.
- @WebServlet
: for servlet class.
- @WebListener
: for listener class.
- @WebFilter
: for filter class.
26)
Which event is fired at the time of project deployment and undeployment?
ServletContextEvent.
27)
Which event is fired at the time of session creation and destroy?
HttpSessionEvent.
28)
Which event is fired at the time of setting, getting or removing attribute from
application scope?
ServletContextAttributeEvent.
29)
What is the use of welcome-file-list?
It
is used to specify the welcome file for the project.
30)
What is the use of attribute in servlets?
Attribute
is a map object that can be used to set, get or remove in request, session or
application scope. It is mainly used to share information between one servlet
to another.
1) What is Spring?
It is a lightweight, loosely
coupled and integrated framework for developing enterprise applications in
java.
2) What are the
advantages of spring framework?
- Predefined Templates
- Loose Coupling
- Easy to test
- Lightweight
- Fast Development
- Powerful Abstraction
- Declarative support
3) What are the
modules of spring framework?
- Test
- Spring Core Container
- AOP, Aspects and Instrumentation
- Data Access/Integration
- Web
4) What is IOC and DI?
IOC (Inversion of Control)
and DI (Dependency Injection) is a design pattern to provide loose coupling. It
removes the dependency from the program.
Let's write a code without
following IOC and DI.
1.
public class Employee{
2.
Address address;
3.
Employee(){
4.
address=new Address();//creating instance
5.
}
6. }
Now, there is dependency
between Employee and Address because Employee is forced to use the same address
instance.
Let's write the IOC or DI
code.
1.
public class Employee{
2.
Address address;
3.
Employee(Address address){
4.
this.address=address;//not creating instance
5.
}
6. }
Now, there is no dependency
between Employee and Address because Employee is not forced to use the same
address instance. It can use any address instance.
5) What is the role of
IOC container in spring?
IOC container is
responsible to:
- create the instance
- configure the instance, and
- assemble the dependencies
6)
What are the types of IOC container in spring?
There
are two types of IOC containers in spring framework.
- BeanFactory
- ApplicationContext
7)
What is the difference between BeanFactory and ApplicationContext?
BeanFactory
is the basic container whereas ApplicationContext is the advanced
container. ApplicationContext extends the BeanFactory interface.
ApplicationContext provides more facilities than BeanFactory such as
integration with spring AOP, message resource handling for i18n etc.
8)
What is the difference between constructor injection and setter injection?
|
No.
|
Constructor Injection
|
Setter Injection
|
|
1)
|
No
Partial Injection
|
Partial
Injection
|
|
2)
|
Desn't
override the setter property
|
Overrides
the constructor property if both are defined.
|
|
3)
|
Creates
new instance if any modification occurs
|
Doesn't
create new instance if you change the property value
|
|
4)
|
Better
for too many properties
|
Better
for few properties.
|
9)
What is autowiring in spring? What are the autowiring modes?
Autowiring
enables the programmer to inject the bean automatically. We don't need to write
explicit injection logic.
Let's
see the code to inject bean using dependency injection.
1. <bean id="emp" class="com.javatpoint.Employee" autowire="byName" />
The
autowiring modes are given below:
|
No.
|
Mode
|
Description
|
|
1)
|
no
|
this is
the default mode, it means autowiring is not enabled.
|
|
2)
|
byName
|
injects
the bean based on the property name. It uses setter method.
|
|
3)
|
byType
|
injects
the bean based on the property type. It uses setter method.
|
|
4)
|
constructor
|
It
injects the bean using constructor
|
The "autodetect" mode is
deprecated since spring 3.
10)
What are the different bean scopes in spring?
There
are 5 bean scopes in spring framework.
|
No.
|
Scope
|
Description
|
|
1)
|
singleton
|
The
bean instance will be only once and same instance will be returned by the IOC
container. It is the default scope.
|
|
2)
|
prototype
|
The
bean instance will be created each time when requested.
|
|
3)
|
request
|
The
bean instance will be created per HTTP request.
|
|
4)
|
session
|
The
bean instance will be created per HTTP session.
|
|
5)
|
globalsession
|
The
bean instance will be created per HTTP global session. It can be used in
portlet context only.
|
11)
In which scenario, you will use singleton and prototype scope?
Singleton
scope should be used with EJB stateless session bean and
prototype scope with EJB stateful session bean.
12)
What are the transaction management supports provided by spring?
Spring
framework provides two type of transaction management supports:
- Programmatic
Transaction Management: should
be used for few transaction operations.
- Declarative
Transaction Management: should
be used for many transaction operations.
»
Spring JDBC Interview Questions
13)
What are the advantages of JdbcTemplate in spring?
Less code:
By using the JdbcTemplate class, you don't need to create connection,statement,start
transaction,commit transaction and close connection to execute different
queries. You can execute the query directly.
14)
What are classes for spring JDBC API?
- JdbcTemplate
- SimpleJdbcTemplate
- NamedParameterJdbcTemplate
- SimpleJdbcInsert
- SimpleJdbcCall
15)
How can you fetch records by spring JdbcTemplate?
You
can fetch records from the database by the query method of JdbcTemplate.
There are two interfaces to do this:
16)
What is the advantage of NamedParameterJdbcTemplate?
NamedParameterJdbcTemplate
class is used to pass value to the named parameter. A named parameter is better
than ? (question mark of PreparedStatement).
It
is better to remember.
17)
What is the advantage of SimpleJdbcTemplate?
The SimpleJdbcTemplate supports
the feature of var-args and autoboxing.
»
Spring AOP Interview Questions
18)
What is AOP?
AOP
is an acronym for Aspect Oriented Programming. It is a methodology that divides
the program logic into pieces or parts or concerns.
It
increases the modularity and the key unit is Aspect.
19)
What are the advantages of spring AOP?
AOP
enables you to dynamically add or remove concern before or after the business
logic. It is pluggable and easy to maintain.
20)
What are the AOP terminology?
AOP
terminologies or concepts are as follows:
- JoinPoint
- Advice
- Pointcut
- Aspect
- Introduction
- Target
Object
- Interceptor
- AOP Proxy
- Weaving
21)
What is JoinPoint?
JoinPoint
is any point in your program such as field access, method execution, exception
handling etc.
22)
Does spring framework support all JoinPoints?
No,
spring framework supports method execution joinpoint only.
23)
What is Advice?
Advice
represents action taken by aspect.
24)
What are the types of advice in AOP?
There
are 5 types of advices in spring AOP.
- Before
Advice
- After
Advice
- After
Returning Advice
- Throws
Advice
- Around
Advice
25)
What is Pointcut?
Pointcut
is expression language of Spring AOP.
26)
What is Aspect?
Aspect
is a class in spring AOP that contains advices and joinpoints.
27)
What is Introduction?
Introduction
represents introduction of new fields and methods for a type.
28)
What is target object?
Target
Object is a proxy object that is advised by one or more aspects.
29)
What is interceptor?
Interceptor
is a class like aspect that contains one advice only.
30)
What is weaving?
Weaving
is a process of linking aspect with other application.
31)
Does spring perform weaving at compile time?
No,
spring framework performs weaving at runtime.
32)
What are the AOP implementation?
There
are 3 AOP implementation.
- Spring AOP
- Apache
AspectJ
- JBoss AOP
»
Spring MVC Interview Questions
33)
What is the front controller class of Spring MVC?
The DispatcherServlet class
works as the front controller in Spring MVC.
34)
What does @Controller annotation?
The @Controller annotation
marks the class as controller class. It is applied on the class.
35)
What does @RequestMapping annotation?
The @RequestMapping annotation
maps the request with the method. It is applied on the method.
36)
What does the ViewResolver class?
The View
Resolver class resolves the view component to be invoked for the
request. It defines prefix and suffix properties to resolve the view component.
37)
Which ViewResolver class is widely used?
The org.springframework.web.servlet.view.InternalResourceViewResolver class
is widely used.
38)
Does spring MVC provide validation support?
Yes.
1) What is PL/SQL?
PL/SQL stands for
procedural language extension to SQL. It supports procedural features of
programming language and SQL both. It was developed by Oracle Corporation in
early of 90's to enhance the capabilities of SQL.
2) What is the purpose
of using PL/SQL?
PL/SQL is an extension of
SQL. While SQL is non-procedural, PL/SQL is a procedural language designed by
Oracle. It is invented to overcome the limitations of SQL.
3) What are the most
important characteristics of PL/SQL?
A list of some notable
characteristics:
- PL/SQL is a block-structured
language.
- It is portable to all environments
that support Oracle.
- PL/SQL is integrated with the
Oracle data dictionary.
- Stored procedures help better
sharing of application.
4) What is PL/SQL
table? Why it is used?
Objects of type tables are
called PL/SQL tables that are modeled as database table. We can also say that
PL/SQL tables are a way to providing arrays. Arrays are like temporary tables
in memory that are processed very quickly. PL/SQL tables are used to move bulk
data. They simplifies moving collections of data.
5) What are the
datatypes available in PL/SQL?
There are two types of datatypes
in PL/SQL:
- Scalar datatypes Example
are NUMBER, VARCHAR2, DATE, CHAR, LONG, BOOLEAN etc.
- Composite datatypes Example
are RECORD, TABLE etc.
6) What is the basic
structure of PL/SQL?
PL/SQL uses BLOCK structure
as its basic structure. Each PL/SQL program consists of SQL and PL/SQL
statement which form a PL/SQL block.
PL/SQL block contains 3
sections.
- The Declaration Section (optional)
- The Execution Section (mandatory)
- The Exception handling Section
(optional)
7) What is the
difference between FUNCTION, PROCEDURE AND PACKAGE in PL/SQL?
Function: The
main purpose of a PL/SQL function is generally to compute and return a single
value. A function has a return type in its specification and must return a
value specified in that type.
Procedure: A procedure
does not have a return type and should not return any value but it can have a
return statement that simply stops its execution and returns to the caller. A
procedure is used to return multiple values otherwise it is generally similar
to a function.
Package: A
package is schema object which groups logically related PL/SQL types , items
and subprograms. You can also say that it is a group of functions, procedure,
variables and record type statement. It provides modularity, due to this
facility it aids application development. It is used to hide information from
unauthorized users.
8)
What is exception? What are the types of exceptions?
Exception
is an error handling part of PL/SQL. There are two type of exceptions:
pre_defined exception and user_defined exception.
9)
How to write a single statement that concatenates the words ?Hello? and ?World?
and assign it in a variable named Greeting?
Greeting
:= 'Hello' || 'World';
10)
Does PL/SQL support CREATE command?
No.
PL/SQL doesn't support the data definition commands like CREATE.
11)
Write a unique difference between a function and a stored procedure.
A
function returns a value while a stored procedure doesn?t return a value.
12)
How exception is different from error?
Whenever
an Error occurs Exception arises. Error is a bug whereas exception is a warning
or error condition.
13)
What is the main reason behind using an index?
Faster
access of data blocks in the table.
14)
What are PL/SQL exceptions? Tell me any three.
- Too_many_rows
- No_Data_Found
- Value_error
- Zero_error
etc.
15)
How do you declare a user-defined exception?
You
can declare the User defined exceptions under the DECLARE section, with the
keyword EXCEPTION.
Syntax:
1. <exception_name> EXCEPTION;
16)
What are some predefined exceptions in PL/SQL?
A
list of predefined exceptions in PL/SQL:
- DUP_VAL_ON_INDEX
- ZERO_DIVIDE
- NO_DATA_FOUND
- TOO_MANY_ROWS
- CURSOR_ALREADY_OPEN
- INVALID_NUMBER
- INVALID_CURSOR
- PROGRAM_ERROR
- TIMEOUT
_ON_RESOURCE
- STORAGE_ERROR
- LOGON_DENIED
- VALUE_ERROR
- etc.
17)
What is a trigger in PL/SQL?
A
trigger is a PL/SQL program which is stored in the database. It is executed
immediately before or after the execution of INSERT, UPDATE, and DELETE
commands.
18)
What is the maximum number of triggers, you can apply on a single table?
12
triggers.
19)
How many types of triggers exist in PL/SQL?
There
are 12 types of triggers in PL/SQL that contains the combination of BEFORE,
AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL keywords.
- BEFORE ALL
ROW INSERT
- AFTER ALL
ROW INSERT
- BEFORE
INSERT
- AFTER
INSERT etc.
20)
What is the difference between execution of triggers and stored procedures?
A
trigger is automatically executed without any action required by the user,
while, a stored procedure is explicitly invoked by the user.
21)
What happens when a trigger is associated to a view?
When
a trigger is associated to a view, the base table triggers are normally
enabled.
22)
What is the usage of WHEN clause in trigger?
A
WHEN clause specifies the condition that must be true for the trigger to be
triggered.
23)
How to disable a trigger name update_salary?
ALTER
TRIGGER update_salary DISABLE;
24)
Which command is used to delete a trigger?
DROP
TRIGGER command.
25)
what are the two virtual tables available at the time of database trigger
execution?
Table
columns are referred as THEN.column_name and NOW.column_name.
For
INSERT related triggers, NOW.column_name values are available only.
For
DELETE related triggers, THEN.column_name values are available only.
For
UPDATE related triggers, both Table columns are available.
26)
What is stored Procedure?
A
stored procedure is a sequence of statement or a named PL/SQL block which
performs one or more specific functions. It is similar to a procedure in other
programming languages. It is stored in the database and can be repeatedly
executed. It is stored as schema object. It can be nested, invoked and
parameterized.
27)
What are the different schemas objects that can be created using PL/SQL?
- Stored
procedures and functions
- Packages
- Triggers
- Cursors
28)
What do you know by PL/SQL Cursors?
Oracle
uses workspaces to execute the SQL commands. When Oracle processes a SQL
command, it opens an area in the memory called Private SQL Area. This area is
identified by the cursor. It allows programmers to name this area and access
it?s information.
29)
What is the difference between the implicit and explicit cursors?
Implicit
cursor is implicitly declared by Oracle. This is a cursor to all the DDL and
DML commands that return only one row.
Explicit
cursor is created for queries returning multiple rows.
30)
What will you get by the cursor attribute SQL%ROWCOUNT?
The
cursor attribute SQL%ROWCOUNT will return the number of rows that are processed
by a SQL statement.
31)
What will you get by the cursor attribute SQL%FOUND?
It
returns the Boolean value TRUE if at least one row was processed.
32)
What will you get by the cursor attribute SQL%NOTFOUND?
It
returns the Boolean value TRUE if no rows were processed.
33)
What do you understand by PL/SQL packages?
A
PL/SQL package can be specified as a file that groups functions, cursors,
stored procedures, and variables in one place.
34)
What are the two different parts of the PL/SQL packages?
PL/SQL
packages have the following two parts:
Specification part: It specifies the part where the interface to the
application is defined.
Body part: This
part specifies where the implementation of the specification is defined.
35)
Which command is used to delete a package?
The
DROP PACKAGE command is used to delete a package.
36)
How to execute a stored procedure?
There
are two way to execute a stored procedure.
From
the SQL prompt, write EXECUTE or EXEC followed by procedure_name.
1. EXECUTE or [EXEC] procedure_name;
Simply
use the procedure name
1. procedure_name;
37)
What are the advantages of stored procedure?
Modularity,
extensibility, reusability, Maintainability and one time compilation.
38)
What are the cursor attributes used in PL/SQL?
%ISOPEN:
it checks whether the cursor is open or not.
%ROWCOUNT:
returns the number of rows affected by DML operations:
INSERT,DELETE,UPDATE,SELECT.
%FOUND:
it checks whether cursor has fetched any row. If yes - TRUE.
%NOTFOUND:
it checks whether cursor has fetched any row. If no - TRUE.
39)
What is the difference between syntax error and runtime error?
A
syntax error can be easily detected by a PL/SQL compiler. For example:
incorrect spelling etc. while, a runtime error is handled with the help of
exception-handling section in a PL/SQL block. For example: SELECT INTO
statement, which does not return any rows.
40)
Explain the Commit statement.
Following
conditions are true for the Commit statement:
- Other
users can see the data changes made by the transaction.
- The locks
acquired by the transaction are released.
- The work
done by the transaction becomes permanent.
41)
Explain the Rollback statement?
The
Rollback statement is issued when the transaction ends. Following conditions
are true for a Rollback statement:
- The work
done in a transition is undone as if it was never issued.
- All locks
acquired by transaction are released.
42)
Explain the SAVEPOINT statement.
With
SAVEPOINT, only part of transaction can be undone.
43)
What is mutating table error?
Mutating
table error is occurred when a trigger tries to update a row that it is
currently using. It is fixed by using views or temporary tables.
44)
What is consistency?
Consistency
simply means that each user sees the consistent view of the data.
Consider
an example: there are two users A and B. A transfers money to B's account. Here
the changes are updated in A's account (debit) but until it will be updated to
B's account (credit), till then other users can't see the debit of A's account.
After the debit of A and credit of B, one can see the updates. That?s
consistency.
45)
What is cursor and why it is required?
A
cursor is a temporary work area created in a system memory
when an SQL statement is executed.
A
cursor contains information on a select statement and the row of data accessed
by it. This temporary work area stores the data retrieved from the database and
manipulate this data. A cursor can hold more than one row, but can process only
one row at a time. Cursor are required to process rows individually for
queries.
46)
How many types of cursors are available in PL/SQL?
There
are two types of cursors in PL/SQL.
- Implicit
cursor, and
- explicit
cursor
1) What are the
components of physical database structure of Oracle database?
Components of physical
database structure are given below.
- One or more data files.
- Two or more redo log files.
- One or more control files.
2) What are the
components of logical database structure in Oracle database?
Components of logical
database structure.
- Tablespaces
- Database's schema objects
3) What is a
tablespace?
A database contains Logical
Storage Unit called tablespaces. A tablespace is a set of related logical
structures. Actually a tablespace groups related logical structures together.
4) What is a SYSTEM
tablespace and when it is created?
When the database is
created in Oracle database system, it automatically generate a SYSTEM named
SYSTEM tablespace. The SYSTEM tablespace contains data dictionary tables for
the entire database.
5) What is an Oracle
table?
A table is basic unit of
data storage in Oracle database. A table contains all the accessible
information of a user in rows and columns.
6) In the Oracle
version 9.3.0.5.0, what does each number shows?
Oracle version number
refers:
- 9 - Major database release number
- 3 - Database maintenance release
number
- 0 - Application server release
number
- 5 - Component Specific release
number
- 0 - Platform Specific release
number
7) What is bulk copy
or BCP in Oracle?
Bulk copy or BCP in Oracle,
is used to import or export data from tables and views but it does not copy
structure of same data.
The main advantage of BCP
is fast mechanism for coping data and you can also take the backup of data easily.
8) What is the
relationship among database, tablespace and data file?
An Oracle database contains
one or more logical storage units called tablespaces. These tablespaces
collectively store whole data of databases and each tablespace in Oracle
database consists of one or more files called datafiles. These datafiles are
physical structure that confirm with the operating system in which Oracle is
running.
9) What is a snapshot
in Oracle database?
A snapshot is a replica of
a target master table from a single point-in-time. In simple words you can say,
snapshot is a copy of a table on a remote database.
10) What is the
difference between hot backup and cold backup in Oracle? Tell about their
benefits also.
Hot
backup (Online Backup): A hot backup is also known as online
backup because it is done while the database is active. Some sites can not shut
down their database while making a backup copy, they are used for 24 hour a
day, 7 days a week.
Cold
backup (Offline Backup): A cold backup is also known as offline
backup because it is done while the database has been shutdown using the
SHUTDOWN normal command. If the database is suddenly shutdown with a uncertain
condition it should be restarted with RESTRICT mode and then shutdown with
NORMAL option.
For a complete cold backup
the following files must be backed up.
All datafiles, All control
files, All online redo log files(optional) and the init.ora file (you can
recreate it manually).
11) How many memory
layers are in the Oracle shared pool?
Oracle shared pools
contains two layers:
- library cache
- data dictionary cache
12) What is save point
in Oracle database?
Save points are used to
divide a transaction into smaller parts. It allows rolling back of a
transaction. Maximum five save points are allowed. It is used to save our data,
whenever you encounter an error you can roll back from the point where you save
your SAVEPOINT.
13) What is hash
cluster in Oracle?
Hash cluster is a technique
to store a data in hash table and improve the performance of data retrieval.
Hash function is applied on table row's cluster key value and store in hash
cluster.
14) What are the
various Oracle database objects?
Tables: This is
a set of elements organized in vertical and horizontal fashion.
Tablespaces: This is
a logical storage unit in Oracle.
Views: It is
virtual table derived from one or more tables.
Indexes: This is
a performance tuning method to process the records.
Synonyms: This is
a name for tables.
15) What is the
difference between pre-select and pre-query?
A pre-query trigger fire
before the query executes and fire once while you try to query. With the help
of this trigger you can modify the where clause part dynamically.
Pre-select query fires
during the execute query and count query processing after Oracle forms
construct the select statement to be issued, but before the statement is
actually issued.
Pre-query trigger fires
before Pre-select trigger.
16) What are the
different types of modules in Oracle forms?
Following are the different
modules in Oracle forms:
- Form module
- Menu module
- Pl/SQL Library module
- Object Library module
17) What is the usage
of ANALYZE command in Oracle?
ANALYZE command is used to
perform various functions on index, table, or cluster. The following list
specifies the usage of ANALYZE command in Oracle:
- It is used to identify migrated
and chained rows of the table or cluster.
- It is used to validate the
structure of the object.
- It helps in collecting the
statistics about object used by the optimizer. They are then stored in the
data dictionary.
- It helps in deleting statistics
used by object from the data dictionary.
18) Can you create a
synonym without having a table?
Yes. We can create a
synonym without having a base table.
19) What types of
joins are used in writing SUBQUERIES?
- Self join
- Outer Join
- Equi-join
20) What is the usage
of control file in Oracle?
In Oracle, control file is
used for database recovery. The control file is also used to identify the
database and redo log files that must be opened for database operation to go
ahead, whenever an instance of an ORACLE database begins.
21) What is a synonym?
A synonym is also known as
alias for a table, view, sequence or program unit.
22) What are the
different types of synonyms?
There are two types of
synonyms or alias:
Private: It
can only accessed by the owner.
Public: It
can be accessed by any database user.
23) What is the usage
of synonyms?
- Synonym can be used to hide the
real name and owner of an object.
- It provides public access to an
object.
- It also provides location
transparency for tables, views or program units of a remote database.
- It simplifies the SQL statements
for database users.
24) How do you store
pictures in a database?
Yes, you can store pictures
in a database using Long Raw Data type. This data type is used to store binary
data for 2 gigabytes of length. However, the table can have only one Long Raw
data type.
25) What is BLOB data
type in Oracle?
BLOB data type is a data
type with varying length binary string. It is used to store two gigabytes
memory. For BLOB data type, the length needs to be specified in bytes.
26) What is the
difference between TRANSLATE and REPLACE in Oracle?
Translate is used to
substitute a character by character while Replace is used to substitute a
single character with a word.
27) What are the
different types of database objects?
A list of different types
of database objects:
- Tables: This is a
set of elements organized in vertical and horizontal fashion.
- Tablespaces: This is a
logical storage unit in Oracle.
- Views: It is
virtual table derived from one or more tables.
- Indexes: This is a
performance tuning method to process the records.
- Synonyms: This is a
name for tables.
28) What is the usage
of Save Points in Oracle database?
Save Points are used to divide
a transaction into smaller phases. It enables rolling back part of a
transaction. There are maximum 5 save points allowed in Oracle Database.
Whenever an error is encountered, it is possible to rollback from the point
where the SAVEPOINT has been saved.
29) What is the
difference between post-database commit and post-form commit?
The post-database commit
trigger is executed after Oracle forms issue the commit to finalized
transaction while, the post-form commit is fired during the post and commit transactions
process, after the database commit occurs.
30) What is Logical
backup in Oracle?
Logical backup is used to
read a set of database records and writing them into a file. An Export utility
is used to take the backup while an Import utility is used to recover from the
backup.
31) What do you
understand by Redo Log file mirroring?
Mirroring is a process of
having a copy of Redo log files. It is done by creating group of log files
together. This ensures that LGWR automatically writes them to all the members
of the current on-line redo log group. If the group fails, the database
automatically switches over to the next group. It diminishes the performance.
32) What is the
meaning of recursive hints in Oracle?
The number of times a
dictionary table is repeatedly called by various processes is known as
recursive hint. Recursive hint is occurred because of the small size of data
dictionary cache.
33) What are the
limitations of CHECK constraint?
The main limitation of
CHECK constraint is that the condition must be a Boolean expression evaluated
using the values in the row being inserted or updated and can't contain sub
queries.
34) What is the use of
GRANT option in IMP command?
GRANT is used to import
object grants.
35) What is the use of
ROWS option in IMP command?
The ROWS option indicates
whether the table rows should be imported.
36) What is the use of
INDEXES option in IMP command?
The INDEXES option is used
to determine whether indexes are imported.
37) What is the use of
IGNORE option in IMP command?
The IGNORE option is used
to specify how object creation errors should be handled.
38) What is the use of
SHOW option in IMP command?
The SHOW option specifies
when the value of show=y, the DDL within the export file is displayed.
39) What is the use of
FILE param in IMP command?
FILE param is used to
specify the name of the export file to import. Multiple files can be listed,
separated by commas.
40) How to convert a
date to char in Oracle? Give one example.
The to_char()
function is used to convert date to character. You can also specify
the format in which you want output.
1. SELECT to_char ( to_date ('12-12-2012', 'DD-MM-YYYY') , 'YYYY-MM-DD') FROM dual;
Or,
1. SELECT to_char ( to_date ('12-12-2012', 'DD-MM-YYYY') , 'DD-MM-YYYY') FROM dual;
41) What are actual
and formal parameters?
Actual
Parameters: Actual parameters are the variables or expressions
referenced in the parameter list of a subprogram.
Let's see a procedure call
which lists two actual parameters named empno and amt:
1. raise_sal(empno, amt);
Formal
Parameters: Formal parameters are variables declared in a subprogram
specification and referenced in the subprogram body.
Following procedure
declares two formal parameters named empid and amt:
1. PROCEDURE raise_sal(empid INTEGER, amt REAL) IS current_salary REAL;
42) What are the
extensions used by Oracle reports?
Oracle reports are use to
make business enable with the facility to provide information of all level
within or outside in a secure way. Oracle report uses REP files
and RDF file extensions.
43) How to convert a
string to a date in Oracle database?
Syntax: to_date (string ,
format)
Let us take an example :
1. to_date ('2012-12-12', 'YYYY/MM/DD')
It will return December
12, 2012.
44) How do you find
current date and time in Oracle?
The SYSDATE()
function is used in Oracle to find the current date and time of
operating system on which the database is running.
1. SELECT TO_CHAR (SYSDATE, 'MM-DD-YYYY HH24:MI:SS') "Current_Date" FROM DUAL;
45) What will be the syntax
to find current date and time in format "YYYY-MM-DD"?
1. SELECT TO_CHAR (SYSDATE, 'YYYY-MM-DD HH24:MI:SS') "Current_Date" FROM DUAL;
73) What is Exception
Handling?
Exception Handling is a
mechanism to handle runtime errors.It is mainly used to handle checked
exceptions.
74) What is difference
between Checked Exception and Unchecked Exception?
1)Checked Exception
The classes that extend
Throwable class except RuntimeException and Error are known as checked
exceptions e.g.IOException,SQLException etc. Checked exceptions are checked at
compile-time.
2)Unchecked Exception
The classes that extend
RuntimeException are known as unchecked exceptions e.g.
ArithmeticException,NullPointerException etc. Unchecked exceptions are not
checked at compile-time.
75) What is the base
class for Error and Exception?
Throwable.
76) Is it necessary
that each try block must be followed by a catch block?
It is not necessary that
each try block must be followed by a catch block. It should be followed by
either a catch block OR a finally block. And whatever exceptions are likely to
be thrown should be declared in the throws clause of the method.
77) What is finally
block?
- finally block is a block that is
always executed.more
details...
78) Can finally block
be used without catch?
- Yes, by try block. finally must be
followed by either try or catch.more
details...
79) Is there any case
when finally will not be executed?
finally block will not be
executed if program exits(either by calling System.exit() or by causing a fatal
error that causes the process to abort).more
details...
80) What is difference
between throw and throws?
|
throw keyword
|
throws keyword
|
|
1)throw
is used to explicitly throw an exception.
|
throws
is used to declare an exception.
|
|
2)checked
exceptions can not be propagated with throw only.
|
checked
exception can be propagated with throws.
|
|
3)throw
is followed by an instance.
|
throws
is followed by class.
|
|
4)throw
is used within the method.
|
throws
is used with the method signature.
|
|
5)You
cannot throw multiple exception
|
You can
declare multiple exception e.g. public void method()throws
IOException,SQLException.
|
81) Can an exception
be rethrown?
Yes.
82) Can subclass
overriding method declare an exception if parent class method doesn't throw an
exception ?
Yes but only unchecked
exception not checked.
83) What is exception
propagation ?
Forwarding the exception
object to the invoking method is known as exception propagation.
Java: String Handling
Interview Questions
There
is given a list of string handling interview questions with short and pointed
answers. If you know any string handling interview question, kindly post it in
the comment section.
84)
What is the meaning of immutable in terms of String?
The
simple meaning of immutable is unmodifiable or unchangeable. Once string object
has been created, its value can't be changed.
85)
Why string objects are immutable in java?
Because
java uses the concept of string literal. Suppose there are 5 reference
variables,all referes to one object "sachin".If one reference
variable changes the value of the object, it will be affected to all the
reference variables. That is why string objects are immutable in java.
86)
How many ways we can create the string object?
There
are two ways to create the string object, by string literal and by new keyword.
87)
How many objects will be created in the following code?
1.
String s1="Welcome";
2.
String s2="Welcome";
3. String s3="Welcome";
Only
one object.
88)
Why java uses the concept of string literal?
To
make Java more memory efficient (because no new objects are created if it
exists already in string constant pool).
89)How
many objects will be created in the following code?
1. String s = new String("Welcome");
Two
objects, one in string constant pool and other in non-pool(heap).
90)
What is the basic difference between string and stringbuffer object?
String
is an immutable object. StringBuffer is a mutable object.
91)
What is the difference between StringBuffer and StringBuilder ?
StringBuffer
is synchronized whereas StringBuilder is not synchronized.
92)
How can we create immutable class in java ?
We
can create immutable class as the String class by defining final class and
93)
What is the purpose of toString() method in java ?
The
toString() method returns the string representation of any object. If you print
any object, java compiler internally invokes the toString() method on the
object. So overriding the toString() method, returns the desired output, it can
be the state of an object etc. depends on your implementation.
Core Java : Nested
classes and Interfaces Interview Questions
94)What
is nested class?
A
class which is declared inside another class is known as nested class. There
are 4 types of nested class member inner class, local inner class, annonymous
inner class and static nested class.
95)
Is there any difference between nested classes and inner classes?
Yes,
inner classes are non-static nested classes i.e. inner classes are the part of
nested classes.
96)
Can we access the non-final local variable, inside the local inner class?
No,
local variable must be constant if you want to access it in local inner class.
97)
What is nested interface ?
Any
interface i.e. declared inside the interface or class, is known as nested
interface. It is static by default.
98)
Can a class have an interface?
Yes,
it is known as nested interface.
99)
Can an Interface have a class?
Yes,
they are static implicitely.
1) What is JDBC?
JDBC is a Java API that is
used to connect and execute query to the database. JDBC API uses jdbc drivers
to connects to the database.
2) What is JDBC
Driver?
JDBC Driver is a software
component that enables java application to interact with the database.There are
4 types of JDBC drivers:
- JDBC-ODBC bridge driver
- Native-API driver (partially java
driver)
- Network Protocol driver (fully
java driver)
- Thin driver (fully java driver)
3) What are the steps
to connect to the database in java?
- Registering the driver class
- Creating connection
- Creating statement
- Executing queries
- Closing connection
4) What are the JDBC
API components?
The java.sql package
contains interfaces and classes for JDBC API.
Interfaces:
- Connection
- Statement
- PreparedStatement
- ResultSet
- ResultSetMetaData
- DatabaseMetaData
- CallableStatement etc.
Classes:
- DriverManager
- Blob
- Clob
- Types
- SQLException etc.
5) What are the JDBC
statements?
There are 3 JDBC
statements.
- Statement
- PreparedStatement
- CallableStatement
6)
What is the difference between Statement and PreparedStatement interface?
In
case of Statement, query is complied each time whereas in case of PreparedStatement,
query is complied only once. So performance of PreparedStatement is better than
Statement.
7)
How can we execute stored procedures and functions?
By using Callable
statement interface, we can execute procedures and functions.
8)
What is the role of JDBC DriverManager class?
The DriverManager
class manages the registered drivers. It can be used to register and
unregister drivers. It provides factory method that returns the instance of
Connection.
9)
What does the JDBC Connection interface?
The Connection
interface maintains a session with the database. It can be used for
transaction management. It provides factory methods that returns the instance
of Statement, PreparedStatement, CallableStatement and DatabaseMetaData.
10)
What does the JDBC ResultSet interface?
The
ResultSet object represents a row of a table. It can be used to change the
cursor pointer and get the information from the database.
11)
What does the JDBC ResultSetMetaData interface?
The
ResultSetMetaData interface returns the information of table such as total
number of columns, column name, column type etc.
12)
What does the JDBC DatabaseMetaData interface?
The
DatabaseMetaData interface returns the information of the database such as
username, driver name, driver version, number of tables, number of views etc.
13)
Which interface is responsible for transaction management in JDBC?
The Connection
interface provides methods for transaction management such as
commit(), rollback() etc.
14)
What is batch processing and how to perform batch processing in JDBC?
By
using batch processing technique in JDBC, we can execute multiple queries. It
makes the performance fast.
15)
How can we store and retrieve images from the database?
By
using PreparedStatement interface, we can store and retrieve images.
1)What is JSP?
Java Server Pages
technology (JSP) is used to create dynamic web page. It is an extension to the
servlet technology. A JSP page is internally converted into servlet.
2) What are the
life-cycle methods for a jsp?
|
Method
|
Description
|
|
public
void jspInit()
|
It is
invoked only once, same as init method of servlet.
|
|
public
void _jspService(ServletRequest request,ServletResponse)throws
ServletException,IOException
|
It is
invoked at each request, same as service() method of servlet.
|
|
public
void jspDestroy()
|
It is
invoked only once, same as destroy() method of servlet.
|
3)What is difference
between hide comment and output comment?
The jsp comment is called
hide comment whereas html comment is called output comment. If user views the
source of the page, the jsp comment will not be shown whereas html comment will
be shown.
4)What are the JSP
implicit objects ?
JSP provides 9 implicit
objects by default. They are as follows:
|
Object
|
Type
|
|
1) out
|
JspWriter
|
|
2)
request
|
HttpServletRequest
|
|
3)
response
|
HttpServletResponse
|
|
4)
config
|
ServletConfig
|
|
5)
session
|
HttpSession
|
|
6)
application
|
ServletContext
|
|
7)
pageContext
|
PageContext
|
|
8) page
|
Object
|
|
9)
exception
|
Throwable
|
5)What is difference
between include directive and include action?
|
include directive
|
include action
|
|
1) The
include directive includes the content at page translation time.
|
1) The
include action includes the content at request time.
|
|
2) The
include directive includes the original content of the page so page size
increases at runtime.
|
2) The
include action doesn't include the original content rather invokes the
include() method of Vendor provided class.
|
|
3) It's
better for static pages.
|
3) It's
better for dynamic pages.
|
6) Is JSP technology
extensible?
Yes. JSP technology is
extensible through the development of custom actions, or tags, which are
encapsulated in tag libraries.
7) How can I implement
a thread-safe JSP page? What are the advantages and Disadvantages of using it?
You can make your JSPs
thread-safe by having them implement the SingleThreadModel interface. This is
done by adding the directive <%@ page isThreadSafe="false" %>
within your JSP page.
8) How can I prevent
the output of my JSP or Servlet pages from being cached by the browser?
(OR) How to disable
caching on back button of the browser?
1.
<%
2.
response.setHeader("Cache-Control","no-store");
3.
response.setHeader("Pragma","no-cache");
4.
response.setHeader ("Expires", "0"); //prevents caching at the proxy server
5. %>
9) How can we handle
the exceptions in JSP ?
There are two ways to
perform exception handling, one is by the errorPage element of page directive,
and second is by the error-page element of web.xml file.
10) What are the two
ways to include the result of another page. ?
There are two ways to
include the result of another page:
11) How can we forward
the request from jsp page to the servlet ?
Yes ofcourse! With the help
of forward action tag, but we need to give the url-pattern of the servlet.
12) Can we use the
exception implicit object in any jsp page ?
No. The exception implicit
object can only be used in the error page which defines it with the isErrorPage
attribute of page directive.
13) How is JSP used in
the MVC model?
JSP is usually used for
presentation in the MVC pattern (Model View Controller ) i.e. it plays the role
of the view. The controller deals with calling the model and the business
classes which in turn get the data, this data is then presented to the JSP for
rendering on to the client.
14) What are context
initialization parameters?
Context initialization
parameters are specified by the <context-param> in the web.xml file,
these are initialization parameter for the whole application and not specific
to any servlet or JSP.
15) What are the
different scope values for the <jsp:useBean> tag?
There are 4 values:
- page
- request
- session
- application
16)What is the
difference between ServletContext and PageContext?-
ServletContext gives the
information about the container whereas PageContext gives the information about
the Request.
17)What is the
difference in using request.getRequestDispatcher() and
context.getRequestDispatcher()?
request.getRequestDispatcher(path)
is used in order to create it we need to give the relative path of the resource
whereas context.getRequestDispatcher(path) in order to create it we need to
give the absolute path of the resource.
18) What is EL in JSP?
The Expression Language(EL)
is used in JSP to simplify the accessibility of objects. It provides many objects
that can be used directly like param, requestScope, sessionScope,
applicationScope, request, session etc.
19)What is basic
differences between the JSP custom tags and java beans?
- Custom tags can manipulate JSP
content whereas beans cannot.
- Complex operations can be reduced
to a significantly simpler form with custom tags than with beans.
- Custom tags require quite a bit
more work to set up than do beans.
- Custom tags are available only in
JSP 1.1 and later, but beans can be used in all JSP 1.x versions.
20) Can an interface
be implemented in the jsp file ?
No.
21) What is JSTL?
JSP Standard Tag Library is
library of predefined tags that ease the development of JSP.
22) How many tags are
provided in JSTL?
There are 5 type of JSTL
tags.
- core tags
- sql tags
- xml tags
- internationalization tags
- functions tags
23) Which directive is
used in jsp custom tag?
The jsp taglib directive.
24) What are the 3
tags used in JSP bean development?
- jsp:useBean
- jsp:setProperty
- jsp:getProperty
25) How to disable
session in JSP?
1. <%@ page session="false" %>
1) What is hibernate?
Hibernate is an open-source
and lightweight ORM tool that is used to store, manipulate and retrieve data
from the database.
2) What is ORM?
ORM is an acronym for
Object/Relational mapping. It is a programming strategy to map object with the
data stored in the database. It simplifies data creation, data manipulation and
data access.
3) Explain hibernate
architecture?
Hibernate architecture
comprises of many interfaces such as Configuration, SessionFactory, Session,
Transaction etc.
4) What are the core
interfaces of Hibernate?
The core interfaces of
Hibernate framework are:
- Configuration
- SessionFactory
- Session
- Query
- Criteria
- Transaction
5) What is
SessionFactory?
SessionFactory provides the
instance of Session. It is a factory of Session. It holds the data of second
level cache that is not enabled by default.
6)
Is SessionFactory a thread-safe object?
Yes,
SessionFactory is a thread-safe object, many threads cannot access it
simultaneously.
7)
What is Session?
It
maintains a connection between hibernate application and database.
It
provides methods to store, update, delete or fetch data from the database such
as persist(), update(), delete(), load(), get() etc.
It
is a factory of Query, Criteria and Transaction i.e. it provides factory
methods to return these instances.
8)
Is Session a thread-safe object?
No,
Session is not a thread-safe object, many threads can access it simultaneously.
In other words, you can share it between threads.
9)
What is the difference between session.save() and session.persist() method?
|
No.
|
save()
|
persist()
|
|
1)
|
returns
the identifier (Serializable) of the instance.
|
return
nothing because its return type is void.
|
|
2)
|
Syn:
public Serializable save(Object o)
|
Syn: public
void persist(Object o)
|
10)
What is the difference between get and load method?
The
differences between get() and load() methods are given below.
|
No.
|
get()
|
load()
|
|
1)
|
Returns null if
object is not found.
|
Throws ObjectNotFoundException if
object is not found.
|
|
2)
|
get()
method always hit the database.
|
load()
method doesn't hit the database.
|
|
3)
|
It
returns real object not proxy.
|
It
returns proxy object.
|
|
4)
|
It
should be used if you are not sure about the existence of
instance.
|
It
should be used if you are sure that instance exists.
|
11)
What is the difference between update and merge method?
The
differences between update() and merge() methods are given below.
|
No.
|
update() method
|
merge() method
|
|
1)
|
Update
means to edit something.
|
Merge
means to combine something.
|
|
2)
|
update()
should be used if session doesn't contain an already persistent state with
same id. It means update should be used inside the session only. After
closing the session it will throw error.
|
merge()
should be used if you don't know the state of the session, means you want to
make modification at any time.
|
Let's
try to understand the difference by the example given below:
1.
...
2.
SessionFactory factory = cfg.buildSessionFactory();
3.
Session session1 = factory.openSession();
4.
5.
Employee e1 = (Employee) session1.get(Employee.class, Integer.valueOf(101));//passing id of employee
6.
session1.close();
7.
8.
e1.setSalary(70000);
9.
10.
Session session2 = factory.openSession();
11.
Employee e2 = (Employee) session1.get(Employee.class, Integer.valueOf(101));//passing same id
12.
13.
Transaction tx=session2.beginTransaction();
14.
session2.merge(e1);
15.
16.
tx.commit();
17. session2.close();
After
closing session1, e1 is in detached state. It will not be in session1 cache. So
if you call update() method, it will throw an error.
Then,
we opened another session and loaded the same Employee instance. If we call
merge in session2, changes of e1 will be merged in e2.
12)
What are the states of object in hibernate?
There
are 3 states of object (instance) in hibernate.
- Transient: The object is in transient state if it is just created
but has no primary key (identifier) and not associated with session.
- Persistent: The object is in persistent state if session is open,
and you just saved the instance in the database or retrieved the instance
from the database.
- Detached: The object is in detached state if session is closed.
After detached state, object comes to persistent state if you call lock()
or update() method.
13)
What are the inheritance mapping strategies?
There
are 3 ways of inheritance mapping in hibernate.
- Table per
hierarchy
- Table per
concrete class
- Table per
subclass
14)
How to make a immutable class in hibernate?
If
you mark a class as mutable="false", class will be treated as an
immutable class. By default, it is mutable="true".
15)
What is automatic dirty checking in hibernate?
The
automatic dirty checking feature of hibernate, calls update statement
automatically on the objects that are modified in a transaction.
Let's
understand it by the example given below:
1.
...
2.
SessionFactory factory = cfg.buildSessionFactory();
3.
Session session1 = factory.openSession();
4.
Transaction tx=session2.beginTransaction();
5.
6.
Employee e1 = (Employee) session1.get(Employee.class, Integer.valueOf(101));
7.
8.
e1.setSalary(70000);
9.
10.
tx.commit();
11. session1.close();
Here,
after getting employee instance e1 and we are changing the state of e1.
After
changing the state, we are committing the transaction. In such case, state will
be updated automatically. This is known as dirty checking in hibernate.
16)
How many types of association mapping are possible in hibernate?
There
can be 4 types of association mapping in hibernate.
- One to One
- One to
Many
- Many to
One
- Many to
Many
17)
Is it possible to perform collection mapping with One-to-One and Many-to-One?
`
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